DE102007028664A1 - Catalyst for the treatment of exhaust gases from diesel or petrol engine in the motor vehicle technology, comprises a metallic monolith having parallel channels along the direction of flow of the exhaust gases, and a heatable jacket pipe - Google Patents

Abstract

The Invention relates to a catalyst for the treatment of exhaust gases, comprising a monolith with a metallic support, the parallel along the flow direction of the exhaust gases Has channels separated by walls are, wherein the walls comprise a metal foam, the is provided with a catalytically active coating, and wherein the mass ratio of metal foam to catalytically active coating between 1: 1 and 20: 1.

Description

The The present invention relates to catalysts for the treatment of Exhaust gases comprising a monolith from a carrier, which consists of a coated metal foam.

such Catalysts are currently being used for the purification of exhaust gases from diesel or gasoline engines used in automotive technology. The catalysts are used in vehicle technology either as Full catalysts or used as coated catalysts. The full catalysts consist of 100 of catalytically active material, whereas coating catalysts consist of a metallic or ceramic carrier with a surface coating consist. A monolithic structure of the catalysts results in the case of the full catalysts by shaping as extrudate. Compared For this purpose, the shape of the coating catalysts by the Carrier specified. Vollextrudates have the advantage that they relatively much active mass for the reaction to be catalyzed can provide and through a porous structure also adsorb gaseous components temporarily and can save. One disadvantage is the relatively bad Heat capacity and associated increased Heating up to operating temperature. For vehicles results from this a reduced catalytic activity during the starting phase (cold start) and resulting increased exhaust emissions.

coated catalysts with metal beams are characterized by the higher Heat capacity of the metal by a material lower heating time to operating temperature off. With that In the case of a cold start of vehicles less exhaust emissions reached. As the catalytic activity usually but also depends on the amount of active material, have coating catalysts Disadvantages.

typically, coating catalysts consist of a carrier material with active coating and temperature-insulated storage in one Casing. The carrier materials are granules and ceramic or metallic monoliths are used. The coatings include, depending on the field of application, a catalytically active metal, such as platinum, palladium, rhodium, nickel, vanadium, Tungsten, etc. as well as high surface area porous metal oxides, by means of a so-called "washcoat", a slurry or dispersion in a fluid phase, on the carrier be applied.

In the present case, catalyst is understood as meaning both so-called diesel oxidation catalysts (DOC), urea hydrolysis catalysts, SCR catalysts (selective catalytic reduction), three-way catalysts or diesel particle filters which catalytically oxidize soot particles. When contacting the exhaust gas emitted from the engine with the catalytically active material, the reaction of unwanted constituents of the exhaust gas takes place. These include carbon monoxide, unreacted hydrocarbons, nitrogen oxides (NO _X ) or soot particles. The carriers are usually in the form of a so-called honeycomb body, which has a large number of channels for fluids, that is to say in particular for gases, and a large surface area for the catalytically active coating.

carrier made of metal have the advantage that they are compared to ceramic ones Heat straps faster. This is shown by catalysts on the basis of metallic carriers a better response under cold start conditions. Furthermore, metallic carriers towards the ceramic a higher mechanical Stability and better formability.

The Metallic carriers are often made of metal sheets or metal foils. This honeycomb body through an alternating arrangement of textured or curved Layers of metal and flat layers made of metal.

Coated metallic supports are known in a variety of variations from the prior art. The DE 37 43 723 discloses, for example, a method for producing a catalyst carrier in which a plurality of corrugated or corrugated and smooth metal layers are superimposed, which are then spirally or involute wound starting from a common center and then secured in a sleeve-shaped shell. This basic shape, ie combination of corrugated and flat metal layers, is realized in a variety of publications.

adversely on the known metallic honeycomb bodies are their smooth Surfaces that compared with ceramic honeycomb bodies are much more difficult to coat insofar as that the coating dispersion, d. H. the washcoat does not adhere well to the smooth metal sheets. In the metallic honeycomb bodies is therefore generally more Binders used to ensure adequate adhesion of the catalytic to achieve active coating on the metal surface.

in the The prior art, however, are not just metallic carriers disclosed, which are characterized by smooth surfaces. They are also metallic foams or metallic fiber materials or wire mesh known which used as support materials become.

So revealed the WO-A-01/28665 a device for removing nitrogen oxides from a fluid flowing through the device, the device comprising a packed structure formed from a sieve-like structure, said sieve-like structure having a porosity of more than 80%. However, the application does not disclose a metallic foam as a carrier for the catalytic coating. Another publication relates to the support material in a catalyst for purifying exhaust gases.

The EP-A-1 063 003 discloses a catalytic structure comprising a base material of an inorganic fiber layer, wherein the layer has the shape of a honeycomb body. The fiber structure serves primarily to improve the adhesion of the catalytic coating.

The DE-A-102 13 937 relates to an apparatus for the selective catalytic oxidation of carbon monoxide. With the aid of the network-type catalysts used, short contact times between the gas to be reacted and a catalytically active coating can be achieved. The disclosed catalysts are essentially full catalysts and not coated catalysts. Coated foam materials are not disclosed.

Further, the US-A-2006/0245987 a thermally conductive porous network coated with a catalyst. The publication describes a multiplicity of porous network structures. These network structures do not include metallic foams having the form of honeycomb bodies.

task the present invention was to provide a catalyst, which has a high heat capacity and has a high thermal conductivity, thus the heating time of the catalyst is low and the heat storage is advantageous. Furthermore, the washcoat on the metallic support adhere well.

The Task is solved by a catalyst for treatment of exhaust gases, which includes a metallic monolith that runs along the flow direction of the exhaust gases parallel channels characterized, which are separated by walls, thereby characterized in that the walls comprise a metal foam, which is provided with a catalytically active coating, wherein the mass ratio of metal foam to the catalytically active coating between 1: 1 and 20: 1, more preferably between 2: 1 and 5: 1, and most preferably 5: 1.

By the use of a metal foam instead of smooth metal sheets or other support materials known in the art will be surprisingly improves the adhesion of the active coating on the metal. Compared to the coating of smooth metal sheets remain with coating of metal foams other amounts of coating on the metal back. The mass ratio is formed from the quotient of the mass of the carrier and the mass of the catalytically active coating after drying and calcination at 1000 ° C.

Metallic foams as used herein are, for example, from DE-A-10 2004 014076 known, to which reference is made in full. However, other metal foams may also be used as the carrier. The term "metal foam" as used herein, thus means a foam material of any metal or any alloy of metals, which may optionally contain other additives such as carbides, etc. The metal foams have a plurality of pores which are interconnected so that a gas can be passed through the foam material.

The Foams can be made, for example, of iron / chromium / nickel alloys or consist of iron / chromium / nickel / aluminum alloys. These Alloys have a good relationship between the parameters strength, brittleness and flexibility.

The Production of such metal foams happens, for example, by mixing metal powder with a metal hydride, which then by hot pressing or extrusion to a molding material be compacted. The molding material is then at a temperature heated above the melting point of the metal, wherein by the Hydride hydrogen is released, whereby the mixture foamed becomes.

Further Possibilities for the production of metal foams are described in the above-mentioned patent application. It can, for. B. a gas are blown into a molten metal, previously made foamable by adding solid ingredients has been. Aluminum alloys typically become stabilized 10-20% by volume of silicon carbide or alumina added.

Due to the surface topography, there is a stronger adhesion of the catalytically active coating on the metal surface, without having to add larger amounts of binders to the coating composition. Due to the GE selected mass ratio, the thermal properties of the coated carrier mainly by the thermal properties of the metal.

According to one preferred embodiment, the thermal conductivity is of the coated metal foam of the catalyst more than 10 W / mK. By the high thermal conductivity becomes an improvement the cold start behavior of the invention Catalysts achieved.

According to the invention the metallic carrier along the flow direction the exhaust gas parallel channels. This means that the Monolith represents a honeycomb body. Because of this structure can warm up the catalyst quickly, so that the catalytic activity after starting the engine quickly is reached.

The parallel channels of the invention metallic carrier can be made by initially flat layers are made of metal foam, which are then provided with wrinkles or made from which Welllagen become. If two corrugated or folded layers are superimposed, so that the direction of the plies or folds in both plies parallel runs parallel, arise in these layer structures parallel Channels through which the exhaust gas flows. Of course the exhaust gas also flows through the porous walls.

According to one preferred embodiment, the monolith comprises a Welllage and a smooth position. Both layers consist of a metallic foam, wherein the corrugated layer is formed by a flat layer Metal foam is curled. When a smooth position is a flat layer of metal foam.

If as in this preferred embodiment, corrugations and Smooth layers are arranged alternately one above the other, it is a procedurally simple way, a To create honeycomb structure.

In a more preferred embodiment, wherein the monolith alternately superimposed corrugated and smooth layers includes, the ratio of wavelength to wave height at the Welllage in the range between 20: 1 to 1:20. Furthermore, the wavelength of the Welllage between 0.5 and 10 mm and the wave height of the corrugated layer between 0.5 and 4 mm.

The Geometry of these corrugations has been in the production of corrugated layers proved to be particularly advantageous. Furthermore, the geometry allows the Welllagen an advantageous coating with catalytically active Material.

According to one Another preferred embodiment of the catalyst the thickness of the walls of the monolith in one area between 0.1 and 5 mm, preferably between 0.5 and 3 mm and most preferably between 1 and 2 mm. Monoliths with these wall thicknesses have a special mechanical stability.

According to one further preferred embodiment of the invention the catalyst is a jacket tube in which the monolith is enclosed. More preferably, the jacket tube is a heatable Jacket tube, with which the heat is supplied to the catalyst can be.

advantage of these embodiments is that the monolith before mechanical Stresses is better protected. By an external Heating allows the coated carrier to the required operating temperature brought to achieve an even better cold start behavior. In one embodiment, the jacket tube may be coated with the Carrier be connected by the components soldered are.

According to a preferred embodiment, the average pore size of the metal foam layers is 450-2,500 μm, preferably 800-1,200 μm. These data refer to the uncoated metallic carrier. According to a further preferred embodiment, the density of the metal foam layers is 0.1-0.9 / cm ³ . Metal foams with these pore dimensions and with this density have proved particularly advantageous in the coating with the catalytically active materials, ie with the washcoat, in that the coating adheres particularly well to the structured surface.

The Object of the present invention is further solved by a catalyst for the treatment of exhaust gases, a metallic Monoliths, which along the flow direction of the Exhaust gases has parallel channels through walls are separated from each other, wherein the walls are a Welllage and a smooth layer comprising a catalytically active coating are provided, wherein either the Welllage or the smooth position a Metal foam include and the mass ratio of metal to catalytically active coating between 1: 1 and 20: 1. According to the invention correspond to the specific embodiments this inventive solution to the embodiments, in which both the smooth position and the Welllage of a metal foam consist.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3743723 [0008]
• WO 01/28665 A [0011]
• - EP 1063003 A [0012]
• - DE 10213937 A [0013]
• US 2006/0245987 A [0014]
• - DE 102004014076 A [0018]

Claims (20)

A catalyst for treating exhaust gases, comprising a metallic monolith having channels parallel to each other along the flow direction of the exhaust gases and separated by walls, characterized in that the walls comprise a metal foam provided with a catalytically active coating Mass ratio of metal foam to catalytically active coating between 1: 1 and 20: 1. Catalyst according to claim 1, characterized in that that the mass ratio of metal foam to catalytic active coating is between 2: 1 and 5: 1. Catalyst according to claim 1, characterized in that that the mass ratio of metal foam to catalytic active coating is 5: 1. Catalyst according to one of the preceding claims, characterized in that the thermal conductivity of the coated metal foam greater than 10 W / mK is. Catalyst according to one of the preceding claims, characterized in that the catalyst comprises a jacket tube, in which the monolith is enclosed. Catalyst according to claim 5, characterized in that that the jacket tube is a heatable jacket tube with which the Catalyst heat can be supplied. Catalyst according to one of the preceding claims, characterized in that the average pore size of the metal foam 450-2,500 microns, preferably 800-1,200 microns is. Catalyst according to one of the preceding claims, characterized in that the density of the metal foam is 0.1-0.9 g / cm ³ . Catalyst according to one of the preceding claims, characterized in that the walls have a thickness in the range between 0.1-5 mm, preferably 0.5-3 mm and most preferably 1-2 mm. Catalyst according to one of the preceding claims, characterized in that the monolith is a Welllage and a Smooth position includes. Catalyst according to claim 10, characterized in that that with respect to the Welllage the ratio of Welllänge to wave height in the range between 20: 1 and 1:20. Catalyst according to claim 10 or claim 11, characterized characterized in that the corrugation length is 0.5-10 mm and the corrugation height is 0.5-4 mm. Catalyst for the treatment of exhaust gases, the one metallic monoliths that runs along the flow direction the exhaust gases has parallel channels through walls are separated from each other, characterized in that the walls a Welllage and a smooth layer, which with a catalytic active coating are provided, wherein either the Welllage or the smooth layer comprise a metal foam and the mass ratio from metal to catalytically active coating between 1: 1 and 20: 1 lies. Catalyst according to claim 13, characterized in that that the mass ratio of metal foam to catalytic active coating is between 2: 1 and 5: 1. Catalyst according to claim 13, characterized in that that the mass ratio of metal foam to catalytic active coating is 5: 1. Catalyst according to one of claims 13 to 15, characterized in that the thermal conductivity of the coated metal is greater than 10 W / mK. Catalyst according to one of claims 13 to 16, characterized in that the catalyst is a jacket tube includes, in which the monolith is enclosed. Catalyst according to claim 17, characterized in that that the jacket tube is a heatable jacket tube with which the Catalyst heat can be supplied. Catalyst according to one of claims 13 to 18, characterized in that the average pore size of the metal foam 450-2,500 microns, preferably 800-1,200 microns is. Catalyst according to one of claims 13 to 19, characterized in that the density of the metal foam is 0.1-0.9 g / cm ³ .